Yes, the black sleeve seems to be some kind of extender. It probably has it's own expander so the sequence is to free the stem's wedge, by re-engaging the bolt, then using that to tap the wedge down then twisting out the stem. Oncethe setm is out, you'll probably (speculating) find a similar arrangement with an expander bolt way down inside, loosen and tap down to free the extender from the fork. (you'll need a long hex key of socket extender, but wait until you see what;s down there.

If it's stuck, use "kroil" or some other "seized bolt loosener oil" between the stem and sleeve, then again if needed between the sleeve and fork.